Flame retardant foamed polyester compositions

ABSTRACT

Normally flammable foamed polyester resins (a) are rendered flame retardant by combination with (b) a flame retardant amount of (i) an aromatic carbonate copolymer, from 25 to 75 wt. % of the repeating units comprising chloro- or bromo-substituted dihydric phenol units; (ii) an aromatic carbonate homopolymer having repeating units comprising chloro- or bromo-substituted dihydric phenol units in combination with an aromatic carbonate homopolymer having repeating dihydric phenol units; or (iii) a combination of (i) with an aromatic carbonate homopolymer having repeating dihydric phenol units, and (c) an antimony-containing compound.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of Ser. No. 233,754, now U.S. Pat. No. 3,833,685.

This invention relates to new and novel flame-retardant foamed polyester compositions. More particularly, it is concerned with foamed flame-retardant high-molecular weight polyesters in combination with flame retardant amounts of aromatic carbonate homopolymers and copolymers, said aromatic carbonates containing at least some chloro- or bromo-substituted dihydric phenol units.

BACKGROUND OF THE INVENTION

High molecular weight polyesters are well known to those skilled in the art.

However, a major short-coming in the use of such polyesters in foamed compositions is their normally highly flammable nature. The flammability of polyesters has been reduced by using halogen-, phosphorus- or nitrogen-containing additives, and such compositions are described in various patents and publications. Flame retarded foamed polyester compositions are desired for many fields of use such as in home construction, automobile and aircraft manufacture, packaging, electrical equipment and the like.

With particular reference to polyesters of the poly(alkylene dicarboxylate) family and related copolyesters, it has been difficult to adequately render such materials flame retardant without sacrificing their inherent, superior properties.

It has now been discovered that if carefully selected families of polycarbonate resins are added to the normally flammable polyesters, alone or in further combination with selected groups of other such polycarbonate resins, there will be provided highly efficiently flame retardant polyester compositions, without any need for reinforcement, yet without modification of physical properties to the extent that they are rendered unuseable for structural applications.

By way of illustration, the addition of a compatible aromatic polycarbonate additive or additives of the type to be described hereinafter, provides compositions which are flame retardant to the point where they meet stringent Underwriter's Laboratory requirements for self-extinguishing compositions.

Moreover, the direct combustibilities of such compositions, as measured in the Oxygen Index Test according to ASTM standard method D-2863, are less than those of controls rendered flame retardant by prior art methods.

It is, accordingly, a principal object of this invention to provide a family of foamable flame-retardant polyester compositions.

Other objects and advantages of the invention will become apparent from the following detailed description.

DESCRIPTION OF THE INVENTION

According to this invention there are provided flame-retardant foamable compositions comprising

a. a normally flammable high-molecular weight polyester; and a flame retardant amount of

b.

i. an aromatic carbonate copolymer in which from 25 to 75 wt. % of the repeating units comprise chloro- or bromo-substituted dihydric phenol units and the remainder of the repeating units comprise dihydric phenol, glycol or dicarboxylic acid units;

ii. an aromatic carbonate homopolymer in which the repeating units comprise chloro- or bromo-substituted dihydric phenol units in combination with an aromatic carbonate homopolymer comprising dihydric phenol units; or

iii. a combination of (i) with an aromatic carbonate homopolymer comprising dihydric phenol units, in combination with

c. a synergist, e.g., an inorganic or organic antimony-containing compound; and

d. a foaming agent.

The term "normally flammable high molecular weight polyester" includes, in general, linear saturated condensation products of diols and dicarboxylic acids, or reactive derivatives thereof. Preferably, they will comprise condensation products of aromatic dicarboxylic acids and aliphatic diols. It is to be understood, that it is also possible to use polyesters such as poly(1,4-dimethylol cyclohexane dicarboxylates, e.g., terephthalates). In addition to phthalates, small amounts of other aromatic dicarboxylic acids, such as naphthalene dicarboxylic acid, or aliphatic dicarboxylic acids, such as adipic acid, can also be present in preferred compositions. The diol constituent can likewise be varied, in the preferred embodiments, by adding small amounts of cycloaliphatic diols. In any event, the preferred polyesters are well known as film and fiber formers, and they are provided by methods outlined in Whinfield, U.S. Pat. No. 2,465,319 and Pengilly, U.S. Pat. No. 3,047,539 and elsewhere. The preferred polyesters will comprise a poly(alkylene terephthalate, isophthalate or mixed isophthalate-terephthalate, e.g., up to 30 mole % isophthalate), said alkylene groups containing from 2 to 10 carbon atoms, e.g., poly(ethylene terephthalate) or poly(1,4-butylene teraphthalate). Because of its rapid crystallization from the melt, it is preferred to use poly(1,4-butylene terephthalate) as the normally flammable polyester resin component of the present compositions.

The molecular weight of the polyester component should be sufficiently high to provide an intrinsic viscosity of about 0.6 to 2.0 deciliters per gram, preferably 0.7 to 1.6 dl./g., measured for example, as a 1% solution in a 60:40 mixture of phenol and tetrachloroethane at 25°C.

As has been mentioned, there will be used in the flame retardant compositions of this invention, the halogen-containing aromatic polycarbonate in combination with a synergist, such as phosphorus compounds, but particularly with inorganic and organic antimony compounds, Such compounds are widely available or can be made in known ways. In preferred embodiments, the type of antimony compound used is not critical, being a choice primarily based on economics. For example, as inorganic antimony compounds there can be used antimony oxide, (Sb₂ O₃); antimony phosphate; KSb(OH)₆ ; NH₄ SbF₆ ; SbS₃ ; and the like. A wide variety of organic antimony compounds can also be used, such as antimony esters with organic acids; cyclic alkyl antimonites; aryl antimonic acids, and the like. Illustrative of the organic antimony compounds, including inorganic salts of such compounds are: KSb tartrate; Sb caproate; Sb(OCH₂ CH₃)₃ ; Sb(OCH(CH₃)CH.sub. 2 CH₃)₃ ; Sb polymethylene glycolate; triphenyl antimony; and the like. Especially preferred is antimony oxide.

In one embodiment of this invention the compositions will include a flame retardant amount of an aromatic carbonate copolymer in which from 25 to 75 wt. % of the repeating units comprise chloro- or bromo-substituted dihydric phenol units and the remainder of the repeating units comprise dihydric phenol, glycol or dicarboxylic acid units. The aromatic carbonate copolymers can be prepared by any of the well known methods which, for example, include reacting such materials as tetrabromobisphenol-A [2,2-bis(3,5-dibromo-4-hydroxyphenyl) propane], or tetrachlorobisphenol-A [2,2-bis(3,5-dichloro-4-hydroxyphenyl) propane], and another compound, such as a glycol, e.g., ethylene glycol or propylene glycol or a dicarboxylic acid, e.g., adipic acid or isophthalic acid, but preferably a dihydric phenol such as bisphenol-A [2,2-bis(4-hydroxyphenyl)propane] with phosgene or a reactive derivative of phosgene. A detailed procedure for the preparation of preferred such copolymers will be set forth hereinafter.

In general, the carbonate copolymer modifier employed to provide the moldable flame-resistant polyester resin-containing compositions of the present invention will be a copolymer prepared by reacting 75-25 wt.% and preferably 40-30 wt.% of tetrabromobisphenol-A or tetrachlorobisphenol-A and correspondingly, 25-75 and preferably 60-70 wt.% of another compound which may be either a dihydric phenol, a glycol or a dicarboxylic acid or mixtures thereof, said weights being based on the total weight of the copolymer. In addition, the aromatic carbonate copolymer should have an intrinsic viscosity of 0.2-0.7 deciliters/gram, as measured, for example, in p-dioxane at about 30°C. Typical examples of the other compounds which can be employed in place of the bisphenol-A component of the copolymer are other dihydric phenols such as hydroquinone, resorcinol, 2,2-bis-(4-hydroxyphenyl)pentane, 2,4'-dihydroxydiphenylmethane, 2,6-dihydroxynaphthalene, bis-(4-hydroxyphenyl)sulfone, 4,4'-dihydroxydiphenyl ether, etc., or glycols, such as ethylene glycol, propylene glycol, tetramethylethylene glycol, etc., and also dicarboxylic acids such as adipic acid, isophthalic acid, sebacic acid, etc.; as well as mixtures of any of the above. However, the preferred copolymer component for use in the practice of this invention is a copolymer of about 35 wt.% of tetrabromobisphenol-A and 65 wt.% of bisphenol-A, respectively.

Although such aromatic carbonate copolymer components can be used in combination with any of the known synergists, such as phosphorus compounds, it is preferred to use inorganic or organic antimony compounds, e.g., antimony oxide as mentioned above, and such combinations are preferred embodiments of this invention.

In another preferred embodiment of this invention, component (b) will comprise, in combination, an aromatic carbonate homopolymer in which the repeating units comprise units of the formula ##SPC1##

wherein R¹ and R² are hydrogen, (lower)alkyl or phenyl, X¹ and X² are bromo or chloro, and m and r are from 1 to 4, the average number of repeating units being from about 2 to about 20, the second component of the combination being an aromatic carbonate homopolymer comprising repeating units of the formula ##EQU1## wherein A is a divalent aromatic radical of the dihydric phenol. Preferably, they will comprise repeating units of the formula ##SPC2##

R¹ and R² being as above defined, the average number of repeating units being at least 100, and preferably from about 100 to about 400.

With respect to such homopolymer components having from about 2 to about 20 repeating units, the preferred compounds will be further characterized in having a low volatility when heated above 200°C.

This can be achieved by balancing the amount of halogen with the number of units in the chain, as is obvious to those skilled in the art. Such compounds can be prepared by reacting a carbonate precursor with a mixture of a halogenated dihydric phenol and a chain stopper. The carbonate precursor may be either a carbonyl halide or a haloformate. Among the carbonyl halides may be mentioned carbonyl bromide, carbonyl chloride (i.e., phosgene), carbonyl fluoride, and the like. Suitable haloformates will include the bis-chloroformate of tetrabromobisphenol-A or the chloroformate of tribromophenol (a chain stopper) all used together with phosgene, and the like. In all cases, phosgene is the preferred reactant for the dihydric phenols.

The halogenated dihydric phenols preferred for use in preparing the homopolymer of 2 to 20 units used in this invention may be of the formula ##SPC3##

wherein X¹, X², R¹, R², m and r are as above defined. In all cases (lower)-alkyl means straight and branched chain alkyl groups of from 1 to 6 carbon atoms. These dihydric phenols can be made in ways known to those skilled in the art, e.g., by the condensation of an unsubstituted or halogen substituted phenol and with the corresponding ketone, see, e.g., U.S. Pat. No. 2,468,982, then this is followed, if desired, by chlorination or bromination of the aromatic rings.

Illustrative of the dihydric phenols most useful in the preparation of the chain-stopped homopolymers of 2 to 20 units used in this invention are: 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane (i.e., tetrabromobisphenol-A); 2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane (i.e., tetrachlorobisphenol-A); bis(2-bromo-4-hydroxyphenyl)methane; bis(2,6-dibromo-4-hydroxyphenyl)methane; 1,2-bis(2,6-dibromo-4-hydroxyphenyl)ethane; 1,1-bis(2-bromo-6-chloro-4-hydroxyphenyl)ethane; 1,1-bis(3,5-dibromo-4-hydroxyphenyl)ethane; 2,2-bis-(2,6-dibromo-4-hydroxyphenyl)pentane; 3,3-bis(3,5-dibromo-4-hydroxyphenyl)hexane; bis(3,5-dibromo-4-hydroxyphenyl)phenylmethane; bis(3,5-dibromo-4-hydroxyphenyl) cyclohexylmethane; 2,2-bis(4-hydroxy-2,3,5,6- tetrabromophenyl)propane; 2,2-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)propane; and the like. Especially suitable and preferred is the commercially available compound tetrabromobisphenol-A.

Those skilled in the art will realize that a wide variety of chain stopper compounds can be used in the preparation of the components of from 2 to 20 repeating units. In all cases, the chain-stopper will be monofunctional and reactive with the end groups of the repeating units. Usually the end groups will be reactive derivatives of a carbonate precursor, as defined above, so that any mono-functional compound capable of reacting with a carbonyl halide, a carbonate ester or a haloformate will suffice. Merely by way of illustration, there can be used organic monohydroxy compounds; as well as carboxylic acids or acid halides and many others. Particularly suitable are organic hydroxy compounds, such as alcohols, e.g., methanol, ethanol, decanol, and the like, and phenols. Particularly preferred as chain stopping compounds are organic phenols and especially preferred are chloro or bromo-substituted phenols. The latter chain stoppers give rise to chain stopped components for use in the present compositions which have terminal substituents of the formulae: ##SPC4##

wherein X³ and X⁴ are bromo or chloro and p and q are each from 1 to 5. The respective phenols can be made in procedures well known to those skilled in the art. Illustrative of such phenols are 2-, 3-, 4-bromophenol and their chloro-analogs; 2,3-, 2,4-, 2,5-, 2,6-, 3,5- and 3,4-dibromophenol and their chloro-analogs; 2,3,5- and 2,4,6-tribromophenol and their chloro-analogs; 2,3,4,6- and 2,3,4,5-tetrabromophenol and their chloro-analogs; and 2,3,4-5,6-pentabromophenol and its chloro-analog. Chloro-bromo compounds can also be used. Especially suitable chain stopping compounds are the trihalogenated phenols and especially preferred is 2,4,6-tribromophenol.

The chain-stopper polymers of carbonates of halogenated dihydric phenols having an average of about 2 to 20 units in the chain are prepared by reacting a carbonate precursor with a mixture of the dihydric phenol and the chain stopper preferably in an inert solvent, and in the presence of an acid acceptor, until condensation is complete. It is necessary to use at least the stoichiometric amount of the carbonate precursor, and preferably an excess. Under such conditions, the ratio of the dihydric phenol to the monofunctional chain stopper will control the number of repeating dihydric phenol-carbonate units in the chain. If 2 moles of dihydric phenol and 2 moles of chain stopper are used, for example, the average number of repeating units, or n, as above defined, will be 2 and the product will have a relatively lower softening point. If, on the other hand, 10 or 20 moles of dihydric phenol and 2 moles of chain stopper are used, the average number of repeating units, n, will be about 10 or 20, as the case may be. It is preferred that the average number of repeating units, n, will be between 3 and 7 and especially preferred that they be of about 5. Accordingly, the molar ratio of dihydric phenol to chain stopper will preferably range from 3-7 to 2, and especially perferably, it will be about 5 to 2. If the product comprises a poly(tetrabromobisphenol-A carbonate), chain-stopped with 2,4,6-tribromophenol, such preferred ranges of repeating units will provide very useful softening points, e.g., from 230° to 260°C. and from 230° to 240°C., respectively. Such compounds will have a high bromine content, i.e., 56-59% and an average molecular weight of about 3000 to 3500.

Used in combination with the homopolymer containing from 2 to 20 repeating units or, in another embodiment, with the aromatic carbonate copolymer, is an aromatic carbonate homopolymer having an average number of repeating units of at least about 100, e.g., from about 100 to about 400, or more. Certain of such polycarbonate resins are commercially available; all of them may be prepared by reacting a dihydric phenol free of halogen substitution with a carbonate precursor such as phosgene, a haloformate or a carbonate ester. Generally speaking, the resulting carbonate polymers may be typified as possessing recurring structural units of the formula: ##EQU2## where A is a divalent aromatic radical of the dihydric phenol employed in the polymer producing reaction. Preferably, the polycarbonate homopolymer resins used with the halogen-containing aromatic carbonate homo-or co-polymers to provide the flame-resistant compositions of this invention will have intrinsic viscosities ranging from about 0.35 to about 0.75, as measured in p-dioxane at about 30°C. Broadly, the dihydric phenols which may be employed to provide such aromatic carbonate homopolymers are mononuclear or polynuclear aromatic compounds, containing as functional groups, two hydroxyl radicals, each of which is attached directly to a carbon atom of an aromatic nucleus. Typical dihydric phenols are 2,2-bis(4-hydroxyphenyl)propane; hydroquinone; resorcinol; 2,2-bis(4-hydroxyphenyl)pentane; 2,4'-dihydroxydiphenyl methane; bis(2-hydroxyphenyl)methane; bis(4-hydroxyphenyl)methane; bis(4-hydroxy-5-nitrophenyl)methane; 1,1-bis(4-hydroxyphenyl)ethane; 3,3-bis(4-hydroxyphenyl)pentane; 2,2'-dihydroxydiphenyl; 2,6-dihydroxy naphthalene; bis(4-hydroxyphenyl)sulfone; 2,2'-dihydroxydiphenyl sulfone; 4,4'-dihydroxydiphenyl ether; and 4,4'-dihydroxy-2,5-diethoxydiphenyl ether. A variety of additional dihydric phenols free of halogen substitution which may be employed to provide such carbonate polymers are disclosed in Goldberg, U.S. Pat. No. 2,999,835. It is, of course, possible to employ two or more different dihydric phenols or, as stated above, a dihydric phenol in combination with a glycol, a hydroxy or acid-terminated polyester, or a dibasic acid in the event a carbonate copolymer rather than a homopolymer is desired for use in combination with the chain-stopped homopolymer in the preparation of the flame-resistant polyester compositions of this invention.

In one convenient manner of preparing the aromatic carbonate polymers of this invention, the dihydric phenol, alone, or mixed with a glycol or dicarboxylic acid or, if used, a chain stopping compound, at the preselected molar ratio, can be added to a well stirred solution of an amine, e.g., triethylamine or pyrridine, in a solvent, such as methylene chloride. Then phosgene gas is introduced into the reaction mixture until an excess is present. A suitable temperature is about 30° to 60°C. and only a short reaction time, e.g., less than 1 hour is needed. The product is recovered, for example, by washing the reaction mixture with water, dilute acid and more water, then pouring the mixture into a large excess of a non-solvent for the polymer, e.g., methanol. The precipitated material can be recovered and dried by conventional methods. Another procedure is to carry out the reaction in a two phase aqueous organic solvent system, e.g., water-methylene chloride, in the presence of a base, such as an alkali metal hydroxide.

The amount of aromatic carbonate copolymer or homopolymer, or mixture thereof, used as a flame-retardant component (b) is not critical to the invention, so long as it is present in a minor proportion based on said compositions--major proportions are uneconomical and may detract from the desired polyester-derived advantages, such as structural integrity, appearance, and the like. However, at least an amount sufficient to render the foamable polyester resin flame retardant, non-burning or self-extinguishing will be used, as the case may be. Those skilled in the art are well aware that the amount of component (b) will vary with the nature of the flammable polyester resin and the relative efficiency of the additive and whether or not a synergist is also present. In general, however, the amount of additive will be from 0.5 to 50 parts by weight per 100 parts by weight of the resinous components, with the lesser amounts providing flame retardancy, and the higher amounts being used for self-extinguishing properties. A preferred range for those compositions based on the aromatic carbonate copolymer will be from about 15 to about 50 parts and an especially preferred range will be from about 20 to about 40 parts of additive per 100 parts of total resinous components in the composition. A preferred range for those compositions emphasizing the chain-stopped aromatic carbonate homopolymer in combination with the aromatic carbonate homopolymer with at least 100 repeating units is from about 15 to about 50 parts by weight (10 to 25 parts of "chain-stopped" and 5 to 25 parts of ">100 repeating units") and especially preferably 15 to 30 (10 to 15 parts of chain-stopped and 5 to 15 parts of >100 repeating units) of the combination per 100 parts by weight of the total resinous components in the composition. With respect to the combination it is preferred that the aromatic carbonate homopolymer of from about 2 to about 20 repeating units comprise from 30 to 70 wt.% and said aromatic carbonate homopolymer of at least about 100 repeating units comprise from 70 to 30 wt. % of the combination, and, especially preferably, from 35 to 55 wt.% and from 65 to 45 wt.%, respectively. The amount of antimony compound can vary over a fairly wide range, but, in general, there is used from about 0.5 to about 20 parts by weight, expressed as antimony oxide, per 100 parts of combined resinous components in the composition, and preferably from about 1 to about 12 parts by weight of antimony oxide. In those embodiments using aromatic carbonate copolymers alone or in combination with an aromatic carbonate homopolymer, the amount of antimony compound will preferably range from 2 to 10 and especially preferably from 3 to 7 parts by weight, per 100 parts by weight of the resinous components in the composition. In the embodiments using chain-stopped aromatic carbonate homopolymers in combination with an aromatic carbonate having at least 100 repeating units, the amount of antimony compound will preferably range from about 2 to about 10 and especially preferably from about 3 to about 7 parts by weight, per 100 parts by weight of the resinous components in the composition. Corresponding molar equivalent amounts of the other antimony compounds can be used. In the combinations of antimony and the aromatic carbonate homopolymers and copolymers contemplated by the invention, the weight ratio in the combination can vary widely, but it is preferred to use from about 0.1 to 1.0 parts of antimony compound for each 1.0 part by weight of the total amount of halogenated carbonate in the composition.

It is also regarded to be among the features of this invention to include in the foamable compositions, other ingredients, such as fillers, pigments, stabilizers, and the like, in conventional amounts for their conventionally employed purposes.

The manner of adding the flame-retardant additives to the polyester resin is not critical; is conventional; and will be obvious to those skilled in the art. Preferably, however, each ingredient is added as part of a blend premix and the latter is mixed, e.g., by passage through an extruder, or by fluxing on a mill, at a temperature dependent on the needs of the particular compositions. The mixed composition can be cooled and cut up into molding granules and foamed by extrusion into any desired shape. Typical foaming techniques will be illustrated hereinafter.

The foamable compositions of the invention may also include fullers or reinforcing fillers, such as aluminum, iron or nickel, and the like and nonmetals, such as carbon filaments, silicates, such as acicular calcium silicate, asbestos, titanium dioxide, potassium titanate and titanate whiskers, glass flakes and fibers and mixtures thereof. It is also to be understood that, unless the filler adds to the strength and stiffness of the composition, it is only a filler and not a reinforcing filler, as contemplated herein. In particular, the reinforcing fillers increase the flexural strength, the flexural modulus, the tensile strength and the heat distortion temperature.

Although it is only necessary to have at least a reinforcing amount of the reinforcement present, in general, the reinforcing filler may comprise from about 5 to about 60 parts by weight of the total composition.

In particular, the preferred reinforcing fillers are of glass, and it is preferred to use fibrous glass filaments comprised of lime-aluminum borosilicate glass that is relatively soda free. This is known as "E" glass. However, other glasses are useful where electrical properties are not so important, e.g., the low soda glass known as "C" glass. The filaments are made by standard processes, e.g., by stream or air blowing, flame blowing and mechanical pulling. The preferred filaments for reinforcement are made by mechanical pulling. The filament diameters range from about 0.003 to 0.009 inch, but this is not critical to the present invention.

In general, best properties will be obtained if the sized filamentous glass reinforcement comprises from about 5 to about 60% by weight based on the combined weight of glass and polyester and preferably from about 10 to about 50% by weight. Especially, preferably the glass will comprise from about 10 to about 40% by weight based on the combined weight of glass and polyester.

It has been found that below 5% by weight of glass, the physical properties of the glass-filled compositions are greatly inferior. Generally, for direct molding use, up to about 60% of glass can be present without causing flow problems. However, it is useful also to prepare the compositions containing substantially greater quantities, e.g., up to 70-80% by weight of glass. These concentrates can then be custom blended with blends of polyester that are not glass reinforced to provide any desired glass content of a lower value.

In preparing the present compositions, it is convenient to use the filamentous glass in the form of chopped strands of from about one-eighth inch to about 1 inch long, preferably less than one-fourth inch long. In structures foamed from the compositions, on the other hand, even shorter lengths will be encountered because, during compounding, considerable fragmentation will occur.

The foaming agents of the present invention can be selected from chemicals containing decomposable groups such as azo, N-nitroso, carboxylate, carbonate, hererocyclic nitrogen containing and sulfonyl hydrazide groups. Representative compounds include azodicarbonamide, dinitrosopentamethylene tetramine, p,p'-oxy-bis-(benzenesulfonyl)-hydrazide, benzene-1,3 disulfonyl hydrazide, azo-bis-(-isobutyionitrile), biuret and urea. The foaming agent can also consist of normally gaseous foaming agents such as gaseous fluorocarbons as well as gases such as nitrogen, carbon dioxide, air, helium, argon and krypton. Volatile liquid foaming agents such as pentane, and liquid fluorocarbons may also be employed in the foaming of the polymer. The foaming agent may be added to the polymer in several different ways which are known to those skilled in the art, for example, by adding liquid or gaseous agents directly to the resin in the extruder while the resin is in the molten state to obtain uniform dispersal of the agent in the molten plastic. The temperature and pressures to which the foamable composition of the invention are subjected to provide a foamed polyester will vary within a wide range, depending upon the amount and type of foaming agent that is used. Preferably, from about 0.02 to about 2.0 weight percent of the foaming agent based on weight of the resin is used. However, higher amounts of foaming agent are within the scope of this invention. The preferred foaming agents are dinitrosopentamethylene tetramine, p-toluene sulfonyl semicarbazide, 5-phenyl-tetrazole, calcium oxalate and trihydrazino-s-triazine.

The polyester resin may be prepared by any of the well known methods outlined above. The filler may be blended with the resin at room temperature. The blend consisting of the polyester resin and the filler is fed into an extruder at a temperature of 440° to about 550°F. The extrudate is then comminuted into pellets or other suitable shapes. If a decomposable chemical foaming agent is used, it can be dry tumbled with the resin. This mixture is then fed into a conventional molding machine. The molding temperature may be from about 440° to about 580°F. with the mold temperature being from about 100° to 250°F., preferably from about 140° to about 200°F. The resulting foam molded product is produced.

If the foaming agent is a liquid or gaseous agent, it may be added directly to the molten resin to obtain uniform dispersal of the agent in the molten resin and thereafter may be injected into a mold to produce a foam molded product.

The foamable composition may be handled in any conventional manner empolyed for the fabrication or manipulation of polyesters such as low and high-pressure injection molding to form products of any desired shape.

PREPARATION OF COMPONENTS FOR THE PREFERRED EMBODIMENTS

The following procedures illustrate methods useful to prepare certain components used in the illustrative examples.

PROCEDURE A 35:65 Aromatic Carbonate Copolymer of Tetrabromobisphenol-A and Bisphenol-A

Tetrabromobisphenol-A, 13.3 g., 0.024 moles, and 10.4 g. of bisphenol-A, 0.046 moles, are added to a well-stirred solution of 10.5 g. of pyridine, 0.13 moles, in enough methylene chloride to give 100 ml. of total solution volume. To the reaction vessel, fitted with a reflux condenser and a thermometer, 5.94 g. of phosgene gas, 0.06 moles, is added at the rate of 1.0 g. per minute through a dip tube below the surface of the solution. The temperature is allowed to rise to 39°C. and the methylene chloride refluxes. After addition of the phosgene is complete, stirring is maintained for about 15 minutes. The reaction solution is then washed with water, dilute HCl, and twice more with water to remove the pyridine, then poured into excess methanol, to precipitate the product. The product is filtered, washed with methanol and air-dried in an oven at 75° to 80°C.; intrinsic viscosity about 0.4 deciliters per gram, measured in dioxane at 30°C.

By the same procedure, substituting tetrachlorobisphenol-A for tetrabromobisphenol-A, there will be obtained the corresponding copolymer with 35 wt.% of chloro-substituted dihydric phenol units. Obviously, variations in the ratios of dihydric phenol starting materials will provide pre-selected ratios of repeating units in the aromatic carbonate copolymer product.

PROCEDURE B Aromatic Carbonate Homopolymer of Bisphenol-A

Procedure A is repeated, using instead of the mixture of tetrabromobisphenol-A and bisphenol-A, 16.0 g. of bisphenol-A, 0.07 moles, alone. After drying, the product has an intrinsic viscosity of about 0.6 deciliters per gram. The average number of repeating dihydric phenol units is above 100.

PROCEDURE C Aromatic Carbonate Homopolymer of Tetrabromobisphenol-A Having About 5 Repeating Units

Procedure A is repeated, using 27.2, 0.05 moles, of tetrabromobisphenol-A and, instead of bisphenol-A, 6.62 g. of tribromophenol, 0.02 moles, as a chain-stopper. After drying there is obtained a 90% yield of a low molecular weight brominated polycarbonate terminated with tribromophenoxy units, which softens at about 230°C., and contains 57.2% by weight of bromine. The average number of repeating units is about 5.

If methanol, phenol and 2,4,6-tribromophenol are substituted for the tribromophenol, there are obtained the corresponding polycarbonates terminated with methoxy, phenoxy and trichlorophenoxy groups. If tetrachlorobisphenol-A is substituted for tetrabromobisphenol-A, the corresponding homopolymer having about 5 repeating chloro-substituted dihydric phenol units per molecule is obtained. If the molar ratio of the dihydric phenol to chain-stopper is changed from 5:2, respectively to 2:2, 10:2 and 20:2, the average number of repeating units in the product is, correspondingly, about 2, about 10 and about 20.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Examples 1-10 describe the preparation of foamable compositions useable to the practice of the invention. Examples 11 and 12 relate to foamed compositions.

EXAMPLE 1

In a 1-inch Wayne extruder operated at 470°F., are blended 65 parts by weight of poly(1,4-butylene terephthalate), intrinsic viscosity 1.03 dl./g., 30 parts by weight of a 35:65 aromatic carbonate copolymer of tetrabromobisphenol-A, and bisphenol-A, intrinsic viscosity about 0.4 dl./g., and 5 parts by weight of antimony oxide. The blended composition is injection molded in a 3 oz. Van Dorn machine at 485°F. into test pieces which are subjected to physical and flame retardancy measurements. The test pieces are self-extinguishing within 5 seconds after two 10-second ignitions by an open flame, with no flaming dripping and a maximum of 10 seconds after-glowing (Rating SE-O, Underwriter's Bulletin 94 Flame Test, method described in Modern Plastics Encyclopedia Vol. 50, No. 10A, P. 665A. The Oxygen Index is 29.0% (ASTM D-2863). By ASTM D-1708, tensile strength is 8830 psi. and elongation at break is 18%. The Izod impact strength is 0.7 ft.-lbs./in. (ASTM D-256) and the ductile impact strength is 350 inch-pounds by the Gardner falling dart method, one-eighth one-eigth inch in thickness.

EXAMPLE 2

The procedure of Example 1 is repeated, the composition in this instance comprising 68 parts by weight of poly(1,4-butylene terephthalate), 26 parts by weight of the 35:65 aromatic carbonate copolymer of tetrabromobisphenol-A and bisphenol-A and 6 parts by weight of antimony oxide. The test pieces are self-extinguishing within 5 seconds after two 10-second ignitions by an open flame, with no flaming dripping and a maximum of 10 seconds after-glowing (SE-O). The Oxygen Index is 29.5%. The tensile strength is 8640 psi. and elongation to break is 23 %. Notched Izod impact strength is 0.7 ft.-lbs./in. and the Gardner ductile impact strength is 350 in.-lbs.

EXAMPLE 3

The procedure of Example 1 is repeated, the composition in this instance comprising 70 parts by weight of poly1,4-butylene terephthalate), 26 parts by weight of the 35:65 aromatic carbonate copolymer of tetrabromobisphenol-A and bisphenol-A and 4 parts by weight of antimony oxide. The test pieces are self-extinguishing within 25 seconds after two 10-second ignitions by an open flame, with release of flaming particles that burn only briefly during the test (Rating SE-2, Underwriter's Laboratories Bulletin 94 Flame Test) and the Oxygen Index is 27.0%. The tensile strength is 9360 psi. and elongation at break is 30%. Notched Izod impact strength is 0.7 ft.-lbs./in. and the Gardner ductile impact strength is 350 in.-lbs.

For comparison purposes, a flame retardant polyester composition is rendered flame retardant with a known halogen-containing agent, the U. L. Bulletin 94 rating being SE-2.

Control Composition A comprises a combination of poly1,4-butylene terephthalate) and a low molecular weight, chain-stopped, highly brominated tetrabromobisphenol-A - phosgene polymerization product (Procedure C, above) and antimony oxide. The results obtained in flammability and physical testing combined with those of Examples 1-3 are set forth in Table 1:

                  Table 1                                                          ______________________________________                                         Flammability Data and Physical Properties of Flame Retardant                   Compositions of Polyesters and Aromatic Polycarbonates                         Example           A*      1       2     3                                      ______________________________________                                         Components (parts by weight)                                                    poly(1,4-butylene tereph-                                                      thalate)         84      65      68    70                                      35:65 aromatic carbonate co-                                                   polymer of TBBPA and BPA**                                                                      --      30      26    26                                      aromatic carbonate homopoly-                                                   mer of TBBPA (5 units)                                                                          13      --      --    --                                      antimony oxide    3       5       6     4                                     Physical Properties                                                             Tensile strength, psi.                                                                          8900    8830    8640  9360                                    Elongation, ult.%                                                                               99      18      23    30                                      Notched Izod impact                                                            strength, ft.-lbs./in.                                                                           0.5     0.7     0.7   0.7                                    Gardner impact, in.-lbs.                                                                        35       350     350   350                                   Flammability Properties                                                         Oxygen Index, %  26      29.0    29.5  27.0                                    U.L. Bulletin 94, 1/16"                                                        flame bar***     SE-2    SE-0    SE-0  SE-2                                   ______________________________________                                           *Control                                                                       **TBBPA -- Tetrabromobisphenol-A; BPA -- bisphenol-A                          ***SE-O, self-extinguishes within 5 sec. (avg.), no flaming dripping;          SE-2, self-extinguishes within 25 sec. (avg.), but releases flaming drips

It should be noted that Control A has extremely low ductile impact strength in comparison with the compositions of Examples 1-3. Although the elongations of Examples 1-3 are lower than the control, the Izod impact strength is also significantly higher and, in fact, is equivalent to that of the unmodified normally-flammable polyester. The Gardner ductile impact strengths of the compositions of Examples 1-3 are also very close to those of the unmodified polyester component. Each of the above-mentioned superior physical properties relates to a different form of toughness, i.e., the Izod test measures the ability to resist shock loading whereas the Gardner test measures ductile instead of brittle failure. Thus the compositions of Examples 1-3 provide workpieces which combine flame retardancy with resistance to both brittle and ductile impact failures.

EXAMPLE 4

In a 1 inch Wayne extruder operated at 460°F. are blended 75.5 parts by weight of poly(1,4-butylene terephthalate), intrinsic viscosity 0.92 dl./g., 8.0 parts by weight of an aromatic carbonate homopolymer of bisphenol-A, intrinsic viscosity, 0.52 dl./g., 13.0 parts by weight of an aromatic carbonate homopolymer of tetrabromobisphenol-A, having an average of 5 repeating units (Procedure C), and 3.5 parts by weight of antimony oxide. The blended composition is injection molded in a 3 oz. Van Dorn machine at 485°F. into test pieces which are subjected to physical and flame retardancy measurements. The test pieces are self-extinguishing within 5 seconds after two 10-second ignitions by an open flame with no flaming dripping and a maximum of 10-seconds after-glowing (Rating SE-O, Underwriters's Laboratories Bulletin 94 Flame Test, Modern Plastics, October, 1970, p. 92-98). The Oxygen Index is 28.0% (ASTM D-2863). By ASTM D-1708, tensile strength is 8790 psi. and elongation at break is 120%. The Izod impact strength is 0.5 ft.-lbs./in. (ASTM D-256) and the ductile impact strength is 168 in.-lbs. by the Gardner falling dart method, sample one-eighth in. in thickness.

EXAMPLES 5 and 6

The procedure of Example 4 is repeated substituting 73.9 and 71.5 parts by weight of the polyester, 9.9 and 12.0 parts by weight of the aromatic carbonate homopolymer of bisphenol-A, 13.0 parts by weight of the aromatic carbonate homopolymer of tetrabromobisphenol-A (5 repeating units) and 3.4 and 3.5 parts by weight of the antimony oxide.

For comparison purposes, Control Composition B is prepared, omitting the aromatic carbonate homopolymer of bisphenol-A. Control Composition B comprises 83.5 parts by weight of poly1,4-butylene terephthalate), 13.0 parts by weight of the aromatic carbonate homopolymer of tetrabromobisphenol-A (5 repeating units) and 3.5 parts by weight of antimony oxide.

The results obtained in flammability and physical testing combined with those of Example 1 are set forth in Table 2:

                  Table 2                                                          ______________________________________                                         Flammability Data and Physical Properties of Flame                             Retardant Compositions of Polyesters and Aromatic                              Polycarbonates                                                                 Example           B*      4       5     6                                      ______________________________________                                         Components (parts by weight)                                                   poly(1,4-butylene terephtha-                                                   late)             83.5    75.5    73.9  71.5                                   aromatic carbonate homopolymer                                                 of BPA**          --       8.0     9.9  12.0                                   aromatic carbonate homopolymer                                                 of TBBPA (5 units)                                                                               13.0    13.0    13.0  13.0                                   antimony oxide     3.5     3.5     3.5   3.5                                   Physical Properties                                                            Tensile strength, psi                                                                            8760    8970    9310  8850                                   Elongation, ult. %                                                                               50       120     107   134                                   Notched Izod impact strength,                                                  ft.-lbs./in.       0.5     0.5     0.5   0.5                                   Gardner impact, in.-lbs.                                                                         72       168     216   112                                   Flammability Properties                                                        Oxygen Index, %   27.0    28.0    27.0  28.0                                   U.L. Bulletin 94, 1/16 " ***                                                                     SE-0    SE-0    SE-2  SE-0                                   ______________________________________                                           *Control                                                                        **BPA -- bisphenol-A; TBBPA -- tetrabromobisphenol-A                         ***SE-0, self-extinguishes within 5 sec. (avg.), no flaming dripping;          SE-2, self-extinguishes within 25 sec. (avg.), but releases flaming drips                                                                               

It should be noted that Control B has lower ductile impact strength in comparison with the compositions of Examples 4-6 and very much lower elongation. Thus these important toughness parameters are not seriously adversely affected in the flame retardant compositions according to this invention.

EXAMPLE 7

In a 21/2 inch Prodex extruder operated at 460°F. are blended 74.0 parts by weight of poly(1,4-butylene terephthalate), intrinsic viscosity, 1.10 dl./g., 10 parts by weight of an aromatic carbonate homopolymer of bisphenol-A, 0.62 dl./g., 13.0 parts by weight of an aromatic carbonate homopolymer of tetrabromobisphenol-A, having an average of 5 repeating units (Procedure C), and 3.0 parts by weight of antimony oxide. The blended composition is injection molded in a 3 oz. Van Dorn machine at 490°F. into test pieces which are self-extinguishing within 25 seconds after two 10-second ignitions, and which drip flaming particles (Rating SE-2, Underwriter's Bulletin 94 Flame Test). The Oxygen Index is 27.0% (ASTM D-2863). By ASTM D-1708, tensile strength is 9240 psi. and elongation at break is 102%. The Izod impact strength is 0.5 (ASTM D-256) and the ductile impact strength is 160 in.-lbs. by the Gardner falling dart method, sample one-eighth in. in thickness.

EXAMPLES 8 and 9

The procedure of Example 7 is repeated, substituting for the aromatic carbonate homopolymer of bisphenol-A, of intrinsic viscosity 0.62, corresponding amounts of the same polymer having intrinsic viscosities, respectively, of 0.52 and 0.45.

For comparison purposes, Control Composition C is prepared, omitting the aromatic carbonate homopolymer of bisphenol-A. Control Composition C comprises 84.0 parts by weight of poly(1,4-butylene terephthalate), 13.0 parts by weight of the aromatic carbonate homopolymer of tetrabromobisphenol-A (5 repeating units) and 3.0 parts by weight of antimony oxide.

The results obtained in flammability and physical testing combined with those of Example 7 are set forth in Table 3:

                  Table 3                                                          ______________________________________                                         Flammability Data and Physical Properties of Flame                             Retardant Compositions of Polyesters and Aromatic                              Polycarbonates.                                                                Examples          C*      7       8     9                                      ______________________________________                                         Components (parts by weight)                                                   poly(1,4-butylene terephtha-                                                   late)             84.0    74.0    74.0  74.0                                   aromatic carbonate homopolymer                                                 of BPA            --      10.0    10.0  10.0                                   aromatic carbonate homopolymer                                                 of TBBPA (5 units)                                                                               13.0    13.0    13.0  13.0                                   antimony oxide     3.0     3.0     3.0   3.0                                   Physical Properties                                                            Tensile strength, psi.                                                                           8900    9240    8920  9170                                   Elongation, ult. %                                                                               99       102     222  94                                     Notched Izod impact strength                                                   ft.-lbs./in.       0.5     0.5     0.5   0.5                                   Gardner impact, in-lbs.                                                                          35       160     320   320                                   Flammability Properties                                                        Oxygen Index, %   26.0    27.0    27.0  27.5                                   U.L. Bulletin 94, 1/16"                                                                          SE-2    SE-2    SE-2  SE-0                                   ______________________________________                                          *Control                                                                 

It should be noted that Control C has very low ductile impact strength (Gardner) in comparison with the compositions of Examples 7-9.

EXAMPLE 10

The procedure of Example 1 is repeated, the composition in this instance comprising 59 parts by weight of poly(1,4-butylene terephthalate), intrinsic viscosity 1.1 dl./g., 10 parts by weight of an aromatic carbonate homopolymer of bisphenol-A, 26 parts by weight of the 35:65 aromatic carbonate copolymer of tetrabromobisphenol-A and bisphenol-A and 5 parts by weight of antimony oxide. The test pieces are self-extinguishing within 5 seconds after two 10-second ignitions by an open flame, with no flaming dripping and a maximum of 10 seconds after-glowing (SE-O). The Oxygen Index is 29.0%. The tensile strength is 8000 psi. and elongation to break is 30%. Notched Izod impact strength is 0.7 ft.lbs./in., and the Gardner ductile impact strength is 200 in.-lbs.

For comparison purposes, two compositions are made in which, respectively, the synergist, antimony oxide, and the aromatic carbonate are omitted. The results obtained in flammability and physical testing combined with those of Example 10 and set forth in Table 4:

                  Table 4                                                          ______________________________________                                         Flammability Data and Physical Properties of Compositions                      of Polyesters and Aromatic Polycarbonates                                      Examples             10      D*      E*                                        ______________________________________                                         Components (parts by weight)                                                   poly(1,4-butylene terephthalate)                                                                    59      74      95                                        aromatic carbonate homopolymer                                                 of BPA               10      --      --                                        35:65 aromatic carbonate copolymer                                             of TBBA and BPA**    26      26      --                                        antimony oxide        5      --       5                                        Physical Properties                                                            Tensile strength, psi.                                                                              8000    8000    8300                                      Elongation, ult. %   30      35      60                                        Notched Izod impact strength                                                   ft.-lbs./in.          0.7     0.6     0.5                                      Gardner impact, in.-lbs.                                                                             200     200     150                                      Flammability Properties                                                        Oxygen Index, %      29.0    24.0    22.5                                      U.L. Bulletin 94, 1/16" flame                                                  bar***               SE-0    fails   fails                                     ______________________________________                                           *Control                                                                       **TBBPA -- tetrabromobisphenol-A; BPA -- bisphenol-A                          ***SE-0, self-extinguishes within 5 sec. (avg.), no flaming dripping.    

It should be noted that both Controls D and E are not flame retardant to the extent that they meet the stringent requirements of the Bulletin 94 flame test. The Notched Izod impact strength of the flame retardant composition of Example 10 is higher than those of the controls and the Gardner ductile impact strength is equal to or higher than the controls. Inspection of the tensile/elongation data reveal that these important properties are retained within commercially acceptable levels if the teachings herein are followed.

In all of the compositions of Examples 4-10, the aromatic carbonate polymer of bisphenol-A has an average number of repeating units of at least 100. With respect to the particular examples, the aromatic carbonate homopolymer about 5 units comprises about 38% in Example 4; 43% in Example 5; 48% in Example 6 and 43% in Examples 7-9 of the total weight of the combination with the aromatic carbonate homopolymer having at least 100 units.

Flame retardant compositions according to this invention are provided if the following substitutions are made in the formulations of Examples 1-10.

For the poly(1,4-butylene terephthalate), substitute poly(ethylene terephthalate), intrinsic viscosity 1.0 dl./g.

For the aromatic carbonate copolymer of tetrabromobisphenol-A and bisphenol-A substitute a copolymer of 35 wt.% tetrachlorobisphenol-A and 65 wt.% of bisphenol-A units; a copolymer of 35 wt.% of tetrabromobisphenol-A and 65 wt.% of propylene glycol units; or a copolymer of 35 wt.% of tetrabromobisphenol-A units and 65 wt.% of sebacic acid units.

For the aromatic carbonate homopolymer of tetrabromobisphenol-A having about 5 repeating units, substitute one having, respectively, about 2 and about 10 repeating units; or substitute an aromatic carbonate homopolymer of tetrachlorobisphenol-A having about 5 repeating units.

In the compositions of Examples 1 to 10, substitute for the antimony oxide stoichiometrical amounts of triphenyl antimony or Sb(OCH₂ CH₃).

EXAMPLES 11-12

Foamed poly(1,4-butylene terephthalate) composition were prepared having the composition noted below:

    Example             F*   11    12                                              __________________________________________________________________________     poly(1,4-butylene terephthalate)                                                                   49.9 49.9  49.9                                            50:50 aromatic carbonate copolymer                                              of TBBPA and BPA (IV 0.35 dl/g in.                                             CHCL.sub.3 at 30°C).                                                                       12.5 12.5  12.5                                            Glass fibers        33.0 33.0  33.0                                            Antimony oxide       4.8  4.8   4.8                                            Stabilizer**         0.2  0.2   0.2                                            Blowing agent        0   nitrogen                                                                              0.25***                                                                 process                                               Physical Properties A    11    12                                              __________________________________________________________________________     Tensile Strength, psi                                                                              17,700                                                                              11,800                                                                               11,800                                          Elongation ultimate %                                                                               3    4     4                                              Heat Deflection temperature at                                                  264 psi             415°F                                                                        380°F                                                                        390°F                                    Notched Izod Impact, ft-lb/in                                                                       1.8 Not   Not                                                                      Applicable                                                                           Applicable                                      Specific Gravity    1.63 1.10  1.10                                            Flammability                                                                   Oxygen Index        28.5 28.5  28.5                                            UL Standard 94, 1/4 inch thick                                                  samples             94V-O                                                                               94V-O                                                                               94V-O                                           __________________________________________________________________________       *Control                                                                       **0.15% Irganox 1093 (Ciba-Geigy), 0.05% Ferro 904 (Ferro Chemicals)          ***Expandex OX-5PT (National Polychemicals Division of Staphan Chemicals)

Although the above examples have shown various modifications of the present invention, other variations are possible in the light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention described which are within the full intended scope of the invention as defined by the appended claims. 

I claim:
 1. A flame retardant composition comprising from 90 to 10 parts by weight of a resinous composition which comprises:a. a normally flammable high molecular weight polyester and a flame-retardant amount of from 0.5 to 50 parts by weight per 100 parts by weight of the resinous components of b.i. an aromatic carbonate copolymer in which from 25 to 75 wt.% of the repeating units comprise chloro- or bromo-substituted dihydric phenol units and the remainder of the repeating units comprise dihydric phenol, glycol or dicarboxylic acid units; ii. an aromatic carbonate homopolymer in which the repeating units comprise chloro- or bromo-substituted dihydric phenol units in combination with an aromatic carbonate homopolymer comprising dihydric phenol units; or iii. a combination of (i) with an aromatic carbonate homopolymer comprising dihydric phenol units, in combination with c. about 0.5 to about 20 parts by weight per 100 parts of combined resinous components in the composition; an inorganic or organic antimony-containing compound; and d. a foaming agent.
 2. A flame retardant composition as defined in claim 1 wherein said normally flammable polyester resin is a poly(alkylene terephthalate, isophthalate or mixed isophthalate-terephthalate), said alkylene groups containing from 2 to 10 carbon atoms.
 3. A flame retardant composition as defined in claim 2 wherein said normally flammable polyester resin is poly(1,4-butylene terephthalate).
 4. A flame retardant composition as defined in claim 1 wherein said aromatic carbonate copolymer or homopolymer is a reaction product of phosgene and a dihydric phenol.
 5. A flame retardant composition as defined in claim 1 wherein aromatic carbonate copolymer component (b) is one in which from 75 to 25 wt.% of the repeating units comprise tetrabromobisphenol-A units and from 25 to 75 wt.% of the repeating units comprise bisphenol-A units.
 6. A flame retardant composition as defined in claim 1 wherein said antimony-containing compound is antimony oxide.
 7. A flame retardant composition as defined in claim 5 wherein, in said aromatic carbonate copolymer, about 35 wt.% of the repeating units comprise tetrabromobisphenol-A units and about 65 wt.% of the repeating units comprise bisphenol-A units, and wherein said copolymer has an intrinsic viscosity of from about 0.2 to about 0.7.
 8. A flame retardant thermoplastic composition comprising from 90 to 10 parts by weight of a resinous composition which comprises:a. a normally flammable high molecular weight poly(1,4-butylene terephthalate); and a flame retardant amount of from 0.5 to 50 parts by weight per 100 parts by weight of the resinous components of b. an aromatic carbonate copolymer in which from 25 to 75 wt. % of the repeating units comprise tetrachlorobisphenol-A or tetrabromobisphenol-A units and from 25 to 75 wt. % of the repeating units comprise bisphenol-A units, and wherein said copolymer has an intrinsic viscosity of 0.2 to 0.7, in combination with c. about 0.5 to about 20 parts by weight per 100 parts by weight of combined resinous components of an organic or inorganic antimony-containing compound and d. a foaming agent.
 9. A flame retardant thermoplastic composition as defined in claim 8 wherein said component (b) contains repeating units of tetrabromobisphenol-A units and bisphenol-A units and comprises from about 15 to about 50 parts by weight of the total resinous components in said composition.
 10. A flame retardant composition as defined in claim 8, wherein said antimony-containing compound is antimony oxide.
 11. A flame retardant composition as defined in claim 9 wherein said polyester component (a) comprises from about 50 to about 85 parts by weight; said aromatic carbonate copolymer component (b) comprises from about 15 to about 50 parts by weight; and said antimony compound comprises from about 2 to about 10 parts by weight, all parts being based on 100 parts by weight of the total resinous components in the composition.
 12. A flame retardant composition as defined in claim 11 wherein said poly(1,4-butylene terephthalate) component (a) comprises from about 60 to about 80 parts by weight; in said aromatic carbonate copolymer component (b) about 35 wt.% of the repeating units comprise tetrabromobisphenol-A units and about 65 wt.% of bisphenol-A units, the amount of component (b) comprises from about 20 to about 40 parts by weight; and the antimony compound comprises antimony oxide, about 3 to 7 parts by weight, all parts being based on 100 parts by weight of the total resinous components in said composition.
 13. A flame retardant composition as defined in claim 1 wherein component (b) (ii) comprises in combination an aromatic carbonate homopolymer in which the repeating units comprise units of the formula ##SPC5##wherein R¹ and R² are hydrogen, (lower) alkyl or phenyl, X¹ and X² are bromo or chloro and m and r are from 1 to 4, the average number of repeating units being from about 2 to about 20 and an aromatic carbonate homopolymer comprising repeating units of the formula ##SPC6## the average number of repeating units being at least
 100. 14. A flame retardant composition as defined in claim 13 wherein said antimony-containing compound is antimony oxide.
 15. A flame retardant composition as defined in claim 13 wherein the units in the homopolymer of from 2 to 20 repeating units are tetrabromobisphenol-A units and the units in the homopolymer of at least 100 repeating units are bisphenol-A units.
 16. A flame retardant composition as defined in claim 13 wherein said aromatic carbonate homopolymer of from about 2 to about 20 repeating units comprises from 30 to 70 wt.% and said aromatic carbonate homopolymer of at least about 100 repeating units comprises from about 70 to about 30 wt.% of said combination.
 17. A flame retardant foamable composition comprising from 90 to 10 parts by weight of a resinous composition which comprises:a. a normally flammable high molecular weight poly(1,4-butylene terephthalate); and a flame retardant amount of from 0.5 to 50 parts by weight per 100 parts of the resinous components of b. an aromatic carbonate homopolymer in which the repeating units comprise tetrabromobisphenol-A units; the average number of repeating units being from about 2 to about 20, in combination with an aromatic carbonate homopolymer in which the repeating units comprise bisphenol-A units; the average number of repeating units being at least about 100, in combination with c. an organic or inorganic antimony-containing compound; and d. a blowing agent.
 18. A flame retardant composition as defined in claim 17, wherein said poly(1,4-butylene terephthalate) component (a) comprises from about 50 to about 85 parts by weight; said aromatic carbonate homopolymer of from about 2 to about 20 repeating units comprises from about 10 to about 25 parts by weight; said aromatic carbonate homopolymer having at least about 100 repeating units comprises from about 5 to about 25 parts by weight, and said antimony compound is antimony trioxide from about 2 to about 10 parts by weight, all parts being based on 100 parts by weight of the total resinous components in said composition.
 19. A flame retardant composition as defined in claim 18 wherein said poly(1,4-butylene terephthalate) component (a) comprises from about 70 to about 85 parts by weight; said aromatic carbonate homopolymer of from about 2 to about 20 repeating units comprises from about 10 to about 15 parts by weight; said aromatic carbonate homopolymer having at least about 100 repeating units comprises from about 5 to about 15 parts by weight and said antimony oxide comprises from about 2 to about 7 parts by weight, all parts being based on 100 parts by weight of the total resinous components in said composition.
 20. A flame retardant composition as defined in claim 19 wherein from 35 to 55 wt.% of said aromatic carbonate homopolymer having from about 2 to about 20 repeating units is combined with from 65 to 45 wt.% of said aromatic carbonate homopolymer having at least about 100 repeating units.
 21. A flame retardant foamable composition as defined in claim 17 wherein said foaming agent is selected from the group consisting of gaseous foaming agents and volatile liquid foaming agents. 